The subject matter disclosed herein relates to variable frequency drives (VFDs), and more specifically to VFDs for driving electric machines used with electric submersible pumps (ESPs) in oil and gas applications.
In typical oil and gas drilling applications a well bore is drilled to reach a reservoir. The well bore may include multiple changes in direction and may have sections that are vertical, slanted, or horizontal. A well bore casing is inserted into the well bore to provide structure and support for the well bore. The oil, gas, or other fluid deposit is then pumped out of the reservoir, through the well bore casing, and to the surface, where it is collected. One way to pump the fluid from the reservoir to the surface is with an electrical submersible pump (ESP), which is driven by an electric motor (e.g., an induction motor or a permanent magnet motor) in the well bore casing.
A variety of components may be used to receive power from a power source, filter, convert and/or transform the power, and then drive the electric motor. For example, a variable frequency drive (VFD) may receive power from a power source (e.g., utility grid, batteries, a generator, etc.). The power may then pass through a filter and a step up transformer before being provided to the electric motor via a cable that passes through the well bore.
In some conditions (e.g., startup of a synchronous motor, seizure of the pump, transient load conditions, etc.), the motor may not operate as intended because magnetic saturation of the transformer prevents adequate voltage from reaching the motor. Accordingly, it may be desirable to improve the system to be capable of providing the motor with sufficient voltage to reduce or eliminate motor stalling.